1. Field of the Invention
The present invention pertains to an optical displacement sensor capable of detecting displacement of a target to which distance is measured by projecting light and receiving such light after reflection thereof.
2. Related Art
Triangulation-type displacement sensors capable of detecting displacement of a target to which distance is measured by projecting light and receiving such light after reflection thereof have been proposed conventionally (e.g., see Japanese Patent Application Publication Kokai No. H4-174923 (1992) and Japanese Patent Application Publication Kokai No. H5-87526 (1993).
FIG. 5 shows a displacement sensor described at Japanese Patent Application Publication Kokai No. H4-174923 (1992).
This displacement sensor consists of light-emitting element 103 for causing light for detection to be projected more or less perpendicularly with respect to distance measurement target 107, light-projecting Fresnel lens 104 arranged in front of light-emitting element 103, light-collecting Fresnel lens 113 for collecting light reflected from distance measurement target 107, and optical position sensing detector (PSD) 110 for detecting light collected by light-collecting Fresnel lens 113, the optical axis of light-collecting Fresnel lens 113 being arranged in a direction perpendicular to the light-receiving surface of PSD 110 and the optical axis of light-projecting Fresnel lens 104.
Furthermore, FIG. 6 shows a displacement sensor described at Japanese Patent Application Publication Kokai No. H5-87526 (1993).
This displacement sensor consists of light-emitting element 120 for causing light for detection to be projected more or less perpendicularly with respect to distance measurement target 117, light-collecting lens (convex lens) 121 arranged in front of light-emitting element 120, pinhole 124 for allowing light reflected from distance measurement target 117 to pass therethrough, and optical position sensing detector (PSD) 122 for detecting light which has passed through pinhole 124, PSD 122 being arranged such that the light-receiving surface thereof is parallel to the optical axis O of the light for detection.
The displacement sensor described at the aforementioned Japanese Patent Application Publication Kokai No. H4-174923 (1992) is such that light-collecting Fresnel lens 113 is used to collect light from light-emitting element 103 when light is projected onto distance measurement target 107. Furthermore, the displacement sensor in Patent Reference No. 2, above, is such that light-collecting lens (convex lens) 121 is used to collect light from light-emitting element 120.
Where light-collecting Fresnel lens 113, light-collecting lens (convex lens) 121, or other such light-collecting element is used, this has presented a problem in that it has been necessary to set the distance between the light-collecting element and the light-receiving element to a prescribed distance; and moreover, the fact that some prescribed size is required for the light-collecting element has caused the dimensions of the overall displacement sensor to increase.
Furthermore, in the case of the displacement sensor described at Japanese Patent Application Publication Kokai No. H4-174923 (1992), light-collecting Fresnel lens 113 is used as means for guiding light reflected from distance measurement target 107 to PSD 110, and this has also contributed to increase in the dimensions of the displacement sensor.
Furthermore, in the case of the displacement sensor described at Japanese Patent Application Publication Kokai No. H5-87526 (1993), pinhole 124 is used as means for guiding light reflected from distance measurement target 117 to PSD 122. Now, it being necessary that the reflected light which is guided by pinhole 124 be incident on the light-receiving surface of PSD 122 in order for detection of that light to occur, the narrowness of that light beam has made it necessary to either increase the precision with which PSD 122 is positioned or increase the dimensions of the light-receiving surface of PSD 122. Furthermore, depending upon the environment in which this displacement sensor is used, dust may accumulate at pinhole 124 or may invade the interior of the sensor from pinhole 124. Under such conditions, it has sometimes occurred that light reflected from distance measurement target 117 is blocked at pinhole 124 or at the sensor interior, impairing the detection capability of the displacement sensor.
The present invention was conceived in order to solve such problems, it being an object thereof to provide an optical displacement sensor which is both thin and small. It is moreover an object thereof to provide an optical displacement sensor whose detection capability is not impaired by dust or the like.